Internal combustion engines such as, for example, gasoline engines combust a mixture of air and fuel to produce a power output. The amount of air and fuel and the ratio of air-to-fuel introduced into a combustion chamber of the engine can affect the power output, efficiency, and exhaust emissions of the engine. Typically, the amount of air introduced into the engine and the ratio of air-to-fuel is controlled by a throttle valve mechanism. The throttle valve mechanism selectively restricts the flow of air into the engine to a flow rate that corresponds to a desired ratio of air-to-fuel. However, by restricting the flow of air into the combustion chamber of the engine, the efficiency of the engine may be reduced. In particular, when the throttle valve is in a flow-restricting position, the engine may have to work harder (e.g., expel additional energy) to draw or pump in the same amount of air as compared to when the throttle valve is in a non-restricting position. This additional work output of the engine decreases the efficiency of the engine.
One attempt to improve the efficiency of an engine has been described in U.S. Pat. No. 6,134,888 (the '888 patent) issued to Zimmer et al. on Oct. 24, 2000. The '888 patent describes an engine having a throttle and an electronic turbocharger control system with a wastegate and a bypass valve. The throttle is disposed between a compressor of a turbocharger and an intake manifold to create a pressure differential. The wastegate is disposed between an engine exhaust duct and a turbine of the turbocharger to divert exhaust gases from the turbine to an exhaust discharge duct, thereby decreasing compressor discharge pressure. The bypass valve is disposed between the compressor and the throttle to connect a compressor discharge duct with the engine exhaust discharge duct, thereby relieving pressure in the compressor discharge duct.
To obtain optimum engine efficiency, the throttle of the '888 patent is maintained in an open position to avoid blocking energy in the form of airflow into the engine. Compressor discharge pressure may be controlled by adjusting a position of the wastegate and the bypass valve. By controlling the compressor discharge pressure, the throttle can be opened to a greater angle, thereby obtaining greater engine efficiency by reducing an exhaust back pressure associated with higher compressor discharger pressures. This increase in throttle angle also reduces energy loss across the throttle, thereby increasing engine efficiency.
Although the system of the '888 patent may increase the efficiency of an engine, it may be complex, expensive, and still lack optimal efficiency. In particular, because the system of the '888 patent requires both a compressor bypass and a wastegate, control of the system may be complicated and component cost of the system substantial. In addition, because the bypass diverts compressed air to the turbine, the energy of the compressed air may either be wasted to the atmosphere via the wastegate, or wastefully directed to driving the turbine for compressing more air. Further, although the wastegate and bypass valve of the electronic turbocharger control system may decrease the amount of restriction associated with the throttle, the throttle of the '888 system is still used throughout the operating range of the engine to inefficiently regulate the flow of air into the engine.
The disclosed air induction system is directed to overcoming one or more of the problems set forth above.